Correlation of Clinical Trachoma and Infection in Aboriginal Communities

Abstract

BackgroundTrachoma is the leading infectious cause of blindness due to conjunctival infection with Chlamydia trachomatis. The presence of active trachoma and evidence of infection are poorly correlated and a strong immunologically-mediated inflammatory response means that clinical signs last much longer than infection. This population-based study in five Aboriginal communities endemic for trachoma in northern Australia compared a fine grading of clinical trachoma with diagnostic positivity and organism load.MethodsA consensus fine grading of trachoma, based on clinical assessment and photograding, was compared to PCR, a lipopolysacharide (LPS)-based point-of-care (POC) and a 16S RNA-based nucleic acid amplification test (NAAT). Organism load was measured in PCR positive samples.ResultsA total of 1282 residents, or 85.2% of the study population, was examined. Taking the findings of both eyes, the prevalence of trachomatous inflammation-follicular (TF) in children aged 1–9 years was 25.1% (96/383) of whom 13 (13.7%) were PCR positive on the left eye. When clinical data were limited to the left eye as this was tested for PCR, the prevalence of TF decreased to 21.4% (82/383). The 301 TF negative children, 13 (4.3%) were PCR positive. The fine grading of active trachoma strongly correlated with organism load and disease severity (rs = 0.498, P = 0.0004). Overall, 53% of clinical activity (TF1 or TF2) and 59% of PCR positivity was found in those with disease scores less than the WHO simplified grade of TF.ConclusionDetailed studies of the pathogenesis, distribution and natural history of trachoma should use finer grading schemes for the more precise identification of clinical status. In low prevalence areas, the LPS-based POC test lacks the sensitivity to detect active ocular infection and nucleic acid amplification tests such as PCR or the 16S-RNA based NAAT performed better. Trachoma in the Aboriginal communities requires specific control measures.

Field evaluation of the CRT and ACON chlamydia point-of-care tests in a tropical, low-resource setting

“…Furthermore, Michel et al found in 201126 that the sensitivity of a similar DRW-manufactured chlamydia lipopolysaccharide POC test for ocular trachoma was 30.4%, substantially less than the 83.6% published earlier by Michel et al 27; the difference was explained by a lower organism load. In an independent study, also published in 2011, Harding-Esch et al 28 found that the sensitivities of this test ranged between 33.3% and 67.9%.…”

Importance of Including Borderline Cases in Trachoma Grader Certification

“…4,6,13,[20][21][22] Photo grading has advantages over field grading. (1) Exam conditions can be standardized.…”

“…2,3 Individual-and community-randomized clinical trials have typically had clinical exam as primary or secondary outcomes. [4][5][6][7][8][9] Unfortunately, grading of clinical trachoma can have considerable variability. Even with rigorous training, different examiners grade cases differently.…”

Trachoma

“…Recent studies continue to find that actual rates of clinical signs in children are higher than actual infection rates. [30, 31]. …”

“…Latent class analysis suggests that clinical signs may be relatively sensitive, but that NAATs are far more specific. [33] Point-of-care (POC) assays of chlamydial lipopolysacchrides have yet to be found reliable in hot, humid environments [30,35]. …”